It is known to render an unexploded munition harmless by cutting through the casing of the munition. Cutting of a large hole itself relieves the pressure and allows the contained explosive to be incinerated without the munition exploding. It is also possible to cut-out and remove the fuse. Because of the danger of the munition exploding while it is being cut, it is important to use a cutting mechanism that can be remotely controlled, to avoid risk of injury to the personnel disposing of the munition. It is also important that the equipment should not have any form of magnetic signature as this could itself set off the munition.
Known equipment for performing this task (somewhat similar to that described in U.S. Pat. No. 4,703,591 though this patent is only concerned with cutting through glass) consists of a frame that can be placed over the unexploded munition and that movably supports a cutting mechanism. The cutting mechanism is a nozzle connected to a high pressure supply of water containing a suspension of abrasive particles such as garnet or olivine.
In the known equipment, the tip of the nozzle always remains in a flat plane. The nozzle is supported on a carrier and can rotate about an axis relative to the carrier to cut a circle in the munition. Furthermore the carrier can be moved in a straight line to allow the cutter to cut another circle or to enable the nozzle to cut in a straight line.
The known mechanism has an important disadvantage in that when cutting along a circle, or along any line transverse to the axis of the cylindrical munition, the distance of the nozzle from the surface of the munition is constantly changing and the movement of the nozzle must therefore be skilfully controlled to reduce the speed of movement of the nozzle as its distance from the cylindrical surface of the munition increases.
Aside from the skill required in controlling the movement of the cutting nozzle, the known mechanism only allows controlled cutting in one dimension. Once a desired line or circle has been cut, the operator must return to the frame and reposition it so that further lines may be cut. This can potentially result in several trips back to the danger area before the munition can be declared safe.
DE 4221666 describes an arrangement intended for cutting through munitions. In this case, the munition is itself rotated beneath the cutting head so that a cut is made around the entire periphery of the munition. Such apparatus is totally unsuited to the deactivation of unexploded munition which are too sensitive to be handled in this way.